Fix a variety of wx related errors

[jmartens]

While running dicompyler from source with the requirements from requirements.txt installed I get a lot of errors, this PR should address them to make dicompyler stop throwing wx related errors.

Among others it fixes:

• wx.lib.pubsub being deprecated in favor of PyPubSub
• fix layout errors for options not valid in horizontal box sizer
• use wx.Cursor in favor of deprecated wx.CursorFromImage()
• remove wxALIGN* where WX_EXPAND is also set

This also incorporates the fixes of #131.

[bastula]

Thanks for working on this. I'll take a look shortly and test out the changes.